Grain moisture tester

ABSTRACT

To provide a lightweight, portable tester, the bottom of an upper cylindrical aluminum container that is the housing for a test cell fits tightly into a lower cylindrical aluminum container that is a base and chassis for electrical circuits that measure permittivity. The upper container has a coaxial cylindrical inner electrode in which a spring scale is mounted, and since the tester is lightweight, the scale is used to measure a sample by weighing the sample along with the entire tester. Polystyrene foam surrounding the inner electrode distributes the sample quite evenly as it is poured into the cell and spaces the grain from the inner electrode to prevent points of concentration of electric field. To compensate for change in permittivity resulting from change in temperature of the sample, a temperature-sensing capacitor is mounted within the cell. A disabling circuit connected to a light-emitting-diode indicator provides a warning that the voltage of a battery is too low to provide reliable readings.

waited States Patent 1 Resin June 12, 1973 GRAIN MOISTURE TESTER [75]Inventor: Roy E. Resh, Bettendorf, Iowa [73] Assignee: AgridustrialElectronics, Inc.,

Bettendorf, Iowa [22] Filed: June 11, 1971 [21] Appl. No.: 152,186

2,266,114 12/1941 Bartlett 324/61 P 1,105,618 8/1914 Christianson 177/50X 3,566,260 2/1971 Johnston 324/61 R 2,774,938 12/1956 Edinborgh 324/61R Primary Examiner-Alfred E. Smith Attorney-Henderson & Strom [57]ABSTRACT To provide a lightweight, portable tester, the bottom of anupper cylindrical aluminum container that is the housing for a test cellfits tightly into a lower cylindrical aluminum container that is a baseand chassis for electrical circuits that measure permittivity. The uppercontainer has a coaxial cylindrical inner electrode in which a springscale is mounted, and since the tester is lightweight, the scale is usedto measure a sample by weighing the sample along with the entire tester.Polystyrene foam surrounding the inner electrode distributes the samplequite evenly as it is poured into the cell and spaces the grain from theinner electrode to pre' vent points of concentration of electric field.To compensate for change in permittivity resulting from change intemperature of the sample, a temperaturesensing capacitor is mountedwithin the cell. A disabling circuit connected to a light-emitting-diodeindicator'provides a warning that the voltage of a battery is too low toprovide reliable readings 13 Claims, 4 Drawing Figures 377/l/////I////l/////////////////////I" IIII/I/Z /I PM'EHIED JUN 1 2 I973INVENTOR.

ROY E. RESH GRAIN Morsruns 'rnsrnn BACKGROUND OF THE INVENTION Thisinvention relates to testers for measuring permittivity of materials andparticularly to testers for measuring the moisture content of grain bymeasuring its permittivity.

Grain-moisture testers of the capacitive type usually comprise a pairelectrodes or parallelplates and electronic means to measurepermittivity of grain by measuring change in capacitance between theelectrodes caused by placing grain between them. Preferably, an outerelectrode is a conductive cylindrical container, and an inner electrodeis a conductive cylinder of smaller diameter mounted coaxially therein.The electrodes are connected to an electronic signal generator, and theeffect of the addition of grain between the electrodes is measured. Incertain testers, the electrodes are connected in a series capacitivecircuit connected to the output of the generator, and a change involtage is measured; in other testers, the electrodes are in the tuningcircuit of the generator, and change in frequency is measured.

In order to obtain reliable test results, the mass of grain placedbetween the electrodes must be the same for successive tests. To obtainequal masses and even distribution of electrical field, the grain shouldbe packed such that it is evenly distributed and pressed together a likeamount for each test. According to U.S. Pat. No. 2,251,64l issued toF.W. Stein on Aug. 5, 1941, a loading device having a hinged cover for abottom is used to measure materials, and the cover is unlatched to filla test cell that is positioned below the loading device. A separateloading funnel is described in U.S. Pat. No. 2,693,575, issued to ILM.Greenwood et al. on Nov. 2, 1954 and the central electrode is coneshapedto alleviate the concentration of electric field at the lower portionsof the cell as a result of packing. Also, a thin plastic sleevesurrounds the central electrode to decrease concentration of field thatresults from electrical contact between the material being tested andthe electrode. Still other testers use spring scales for weighing only aseparate hopper to determine the amount of material to be conveyed fromthe hopper to the test cell.

SUMMARY OF THE INVENTION An object of this invention is to provide amoisture tester that is reliable, and that is easier to use, and moreeconomical to manufacture than prior testers.

A tester according to this invention is easy to use because the testcell can be loaded directly with an exact amount to provide reliablereadings. Loading merely requires the pouring of the material to betested directly into the cell while the cell and an attached measuringcircuit are supported and weighed by a spring scale. In order to weighthe material in this manner, the entire tester is lightweight.

The housing of the tester comprises two cylindrical, aluminum containersor cans; the bottom of an upper container fits tightly into the top of alower container. The upper container is the outer electrode of the testcell and the lower container is the chassis for the required electroniccircuit. A coaxial inner electrode of the cell extends upwardly from aninsulated bottom in the upper container, and it contains a spring scalefor weighing the entire tester and the sample while it is being pouredinto the cell. A plastic foam insulator surrounding the wall of theinner electrode insures reliable reading when a test cell is filled bythis easy method. The insulator is quite thick and has a dielectricconstant not much greater than one in order to prevent concentration offield at points near the inner electrode. The amount of surface frictionoffered by the insulator that is preferably made from closed-cellpolystyrene foam, aids in the even distribution of grain while it isbeing poured into the cell.

The electrical circuit housed in the lower container includes a signalgenerator having its output connected through a series resistor to thetest cell. The series resistor and potentiometers in the test circuitcontribute to easy calibration. A circuit for determining thresholdvoltage includes a Schmitt trigger circuit having an alternating-currentcontrol circuit. The use of alternating-current voltage for triggeringprovides a definite threshold point. At the point of threshold, thetrigger circuit applies signal through a transistor to a lightemittingdiode used as an indicator. A circuit for biasing this transistor ispart of a circuit for disabling the tester when the voltage of thesource of supply drops below the level at which the tester will operateaccurately. To compensate for change in temperature, atemperature-compensating capacitor is connected across the cell and ismounted directly in the cell to acquire the same temperature as thematerial that is being tested.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top oblique view of thegrain moisture tester of this invention;

FIG. 2 is a view of the tester showing the test cell disengaged from itsbase that contains electronic circuits;

FIG. 3 is a diametral cross-section of the assembled grain moisturetester; and

FIG. 4 is a schematic wiring diagram of the circuits for measuringpermittivity.

DESCRIPTION OF TI-IE PREFERRED EMBODIMENT The grain moisture testershown in FIG. 1. has two aluminum, cylindrical containers that functionas a base 12 and a test cell 1 1. The diameters of the containers differenough to provide a tight fit as the bottom portion of the test cell 1 lis pressed into the top portion of the base 12. The vertical wall 13 ofthe test cell 11 is the outer electrode, and the inner electrode 14 isan aluminum container mounted coaxially within the wall 13. Electricalcircuits for determining capacitance between the electrodes are mountedin the base 12.

The test cell 11 can be readily pulled from the base 12 as shown in FIG.2 to provide access to circuit components. A plurality of rivets 15 maybe spaced apart on a circumference near the bottom of the vertical wall13 of the test cell to provide a desirable amount of fric tion and goodelectrical contact between the outer wall of the test cell 11 and theinside surface of the wall of the base 12 as they are pressed together.As the cell 11 is pressed into the base 12, a banana plug 16 mounted onthe axis of the test cell 1 l engages its mating socket 17 mounted onthe axis of the base 12 to complete a circuit between the innerelectrode 14 and the electrical measuring circuits in the base 12.

A spring scale 18 of FIG. 1 has a scale that extends upwardly from theaxis of the inner electrode 14. This scale facilitates measurement of asample to be placed in the annular space between the electrodes of thecell 11. in order for the measurement of permittivity to be accurate,the amount of material added to the cell 11 must be a specific amountfor which the electrical circuits are calibrated, and also the materialmust be packed for every sample in about the same manner. Since thegrain moisture tester is compact and the containers and electrodes arealuminum, the complete tester is light enough to permit the accuratedetermination of the amount of sample by simply weighing the sample andthe complete tester together. The tester is filled while supporting itby the handle 29 of the spring scale 18 as material to be tested isadded until a selected calibration mark appears on the scale. Obviously,after a test reading, the tester is inverted to pour out the sample.

The accuracy of the reading is dependent upon the evenness of thepacking of the material to be tested, and particularly upon the packingclose to the inner electrode 14. Prior testers have used thin insulatingmaterial about the inner electrode to prevent close contact with theelectrode and thereby to decrease concentration of the field at thepoints of greatest contact. In this tester, a thick layer of insulatingmaterial 19 having a dielectric constant not much greater than onecovers the outer surface of the inner electrode 14. For best results,the ratio of the thickness of the insulator to the radius of the innerelectrode 13 should be about 1:11.

The insulator is preferably made from polystyrene foam. The closed-celltype of foam is required to exclude moisture and to provide a desirableamount of friction between the foam and the grain that is to be tested.Not only does the thickness of the insulator and its low dielectricconstant greatly decrease errors caused by points of concentration ofthe electric field about the inner electrode, but the physicalresistance offered by the surface of the closed-cell polystyrene foamhelps distribute the grain evenly about the electrode and furtherdecrease variation in intensity of the field.

The mounting for the inner electrode 14 and the spring scale 18 is shownin the cross-sectional view of FIG. 3. The bottom of that portion of thetest cell that is to receive a sample is a cylindrical disk 20 ofinsulating material mounted above the aluminum bottom of the test cellhousing on a plurality of insulating phenolic spacers 21. The spacersare mounted at equal radial distances from the center of the disk 20,and the upper ends of the spacers 21 may also be used to receivemounting screws attached to the lower edge of the inner electrode 14.The inner electrode is thereby rigidly mounted coaxially within theouter electrode to maintain stable calibration.

The spring scale 18 has a tubular housing 22 mounted axially through theinner electrode 14. The upper end of the housing 22 has an externalthreaded portion extending through a hole in the enclosed top of theinner electrode 14 where it is secured by a nut 23. The housing 22 isalso constrained from lateral movement where it passes through a centerhole in the insulated bottom 20 of the cell. The lower end of thehousing 22 has an internal thread for mounting the banana plug 16 sothat it extends downwardly to engage socket 17 within the base 12. Acalibrated coil spring 24 has a lower end hooked into an eye of aterminal 25 connected to the screw fitting of the banana plug 16. The

upper end of the spring 24 is hooked to the lower terminal of a swivel26, and the upper end of the swivel is hooked to the eye of a terminal27 extending from the lower end of a calibrated, round rod 28 that has acircumferential scale marked on it. The top of the nut 23 has a centralhole with a diameter smaller than the inside diameter of its threadedportion that engages the housing 22, and the upper end of the rod 28 isan easy sliding fit within the hole. A handle 29 is fastened to the topof the scale rod 28 for supporting the tester while the sample to betested is added to the test cell 11. The

bottom of the handle 29 contacts the top of the nut 23 to function as astop in the downward direction of the scale rod. The swivel 26 may be ofthe type used with fishing equipment. The swivel permits the moisturetester to be rotated while it is supported by its handle 29 withoutchanging the calibration of the spring 24.

Suitable circumferential marks 30 and 31 are placed on the rod toindicate a predetermined weight when they appear at the top of the nut.For example, the mark 30 may be placed to appear when the material inthe test cells weighs five ounces, and the mark 31 placed to indicateeight ounces. The marks are visible regardless of the angle of rotationof the tester with respect to the operator.

The cylindrical construction of the cell, the rugged mounting of theinner electrode, the isolated mounting of the electrical connection tothe cell, and the use of a temperature-compensating capacitor mountedwithin the cell contribute to the accuracy of the readings andreliability of the calibration of the moisture tester over long periods.The inner electrode 14 is connected to the electrical test circuit inthe base 12 through the top of the electrode and the housing 22 of thespring scale to the banana plug 16 that extends below the test cell forengaging the receptacle 17. A hole 32 in the bottom of the test cell asshown in FIG. 2 has sufficient diameter to keep the stray capacitance tosuch a low amount that it has negligible effect on the operation of thegrain moisture tester.

The use of the temperature-compensating capacitor 33 shown in FIG. 3simplifies operation of the tester and eliminates the reference totemperature in charts in which moisture content is tabulated fordifferent readings of a calibrated control. As shown, the capacitorextends upward into the bottom portion of the test cell where it is incontact with the material being tested. The value of the capacitor is 22picofarads and is about equal to the value of capacitance between theelectrodes l3 and 14 of the test cell during operation. The temperaturecharacteristic of the capacitor 33 has been chosen to compensate for thechange in permittivity of grain with change in temperature.

Other than a calibrated potentiometer 34, the component parts of theelectrical measuring circuit within the base 12 are mounted on acircular, glass epoxy circuit board 35 of FIG. 3. The board is mountedparallel to the bottom of the base by a plurality of hex spacers 36secured thereto. The center electrode 14 is connected through the bananajack 16 to the electrical test circuit, and the outer electrode 13 thatis the outer housing of the test cell is connected through the rivets 15to the housing of the base 12, the housing being the common circuit ofthe test circuit.

The calibrated potentiometer 34 is mounted near the bottom of the testerthrough the cylindrical wall of the base 12. A solid-state indicatorlight 37 is mounted on the circuit board 35 above the potentiometer 34close behind a small opening 38 (FIG. 1) directly above a calibratedknob 39 of the potentiometer.

The electrical circuit of FIG. 4i includes a signal generator having atransistor 40 for applying signal through a series resistor 41 to theelectrodes of the test cell 11. The proportion of the total signalvoltage appearing across the cell is dependent on the moisture contentof grain or other material placed in the cell. The level of voltageappearing across the cell is measured by adjusting a calibratedpotentiometer 34 to obtain a predetermined level of output at its arm.This predetermined level is just sufficient to operate a Schmitt triggercircuit comprising the transistors 42 and 43. Operation of the Schmitttrigger circuit causes the light-emitting diode 37 to be illuminated toindicate that the arm of the potentiometer 34 has been rotated to aposition where the threshold voltage has been reached.

In more detail, the transistor 40 is connected in a conventionalColpitts oscillator circuit for developing a signal of 7OKHZ, and signalfrom the oscillator is applied through an isolating, emitter-followerstage including the transistor 44 to a series circuit for dividing theoutput voltage of the oscillator according to the capacitance betweenthe electrodes 13 and M of the cell 11. The series circuit comprises thevoltage-dropping resistor 41, a coupling capacitor 45, the banana plugand jack l6 and 17, and the test cell It as a capacitor including theparallel temperature-compensating capacitor 33.

A three-stage amplifier including the transistors 46, 47, and 48 has itinput connected across the electrodes 13 and 14 of the test cell 11through the capacitor 45 and through the common return circuit providedby the outer walls of the containers of the cell ll 1 and the base 12.The first stage of the amplifier is an emitterfollower type having apotentiometer 49 and a resistor 50 in series in the emitter circuit ofthe transistor 46. The potentiometer 49 determines the maximum signallevel to be applied through the succeeding, calibrated potentiometer 34.Signal from the arm the potentiometer 49 is applied to the input of asecond stage having the calibrated potentiometer 34 in the emittercircuit of the transistor 47 in series with a resistor 51 and a variableresistor 52. The adjustment of the resistor 52 provides the proper rangeof the potentiometer 34 to agree with its calibrated dial. The thirdstage has the transistor 48 connected in an emitter-follower arrangementwith its input being connected to the arm of the potentiometer 341 andits output capacitively coupled to the base of the transistor 42 of theSchmitt trigger circuit.

The potentiometer 34 is calibrated to indicate change in capacitancebetween the electrodes 13 and M of the test cell 11 according to itsscale and the readings on a chart for moisture content of grain. First,the knob 39 of the potentiometer 341 is rotated to a position formaximum reading and while a reference capacitor having a capacitanceequal to the maximum capacitance to be measured is substituted for thetest cell 11, the potentiometer 49 is adjusted to the point where theindicator light just turns on. In a like manner, the knob 39 is set forminimum reading and while a different reference capacitor having acapacitance equal to the capacitance for minimum moisture content issubstituted for the cell, the variable resistor 52 is adjusted. Althoughthe adjustable potentiometer 49 and the resistor 52 are mounted on thecircuit board 35 (FIG. 3), they are readily accessible for adjustmentbecause each is positioned opposite a respective one of the rubber feet53 inserted in holes in the bottom of the base 12. While the respectiverubber foot is removed, the adjustment can be made readily by a screwdriver.

To obtain a reading of permittivity for a sample of grain within thetest cell, the dial of the potentiometer 34 is rotated from a positionthat provides minimum signal voltage at the output of the transistor 48in the direction of increasing voltage until the Schmitt trigger circuit(transistors 42 and d3) just starts to operate as indicated byillumination of the light-emitting diode 37. The Schmitt trigger circuitis conventional, but rather than using direct-current voltage fortriggering, alternating-current voltage from the output of thetransistor 48 of the amplifier stage is applied to the base circuit ofthe transistor 42. By using altemating-current voltage, the threshold issharper in that the Schmitt trigger circuit starts operation at veryclose to the same voltage every time.

The output of the Schmitt trigger circuit is applied to the base circuitof a transistor 54, and the emitter of the transistor 54 is connected toa filter capacitor 55 and also through a resistor 56 to the base of atransistor 57. The transistor 54 becomes conductive only during thepositive peaks of the wave form of the output of the Schmitt triggercircuit so that only short bursts of current are conducted from theemitter of the transistor 54 to the capacitor 55. The capacitor hassufficient capacitance to filter the voltage derived from the peaks ofcurrent so that the transistor 57 is maintained conductive while theSchmitt trigger circuit is operating. The path of the current forilluminating the light-emitting diode 37 can be traced from the positiveterminal of the battery 58, through the off-on switch 59, thelightemitting diode 37, a resistor 60, the emitter-collector circuit ofa transistor 61, through the emitter-collector circuit of the transistor57 and the common-retum circuit to the negative terminal of the battery58. An advantage of using the light-emitting diode 37 is its low drainon the battery 58.

After the voltage of the battery 58 becomes low but before it dropsbelow a level at which the circuit for measuring permittivity becomesunreliable, the bias voltage on the base of the transistor 61 is removedto disable the circuit connected to the light-emitting diode 37. Acircuit for supplying direct current extends from the switch 559 throughthe dropping resistor 62 to the positive supply line 64 of all theelectrical circuits except the circuit of the light-emitting diode. Thevoltage on this line is regulated by the Zener or breakdown diode 63connected between the line and the common return circuit. The biascircuit for the transistor 61 does not include the resistor 62 for it isconnected to the battery directly through the off-on switch 59, and itincludes a Zener diode 65, a resistor 66, and a resistor 67 in a seriescircuit connected across the battery. The base of the transistor 61 isconnected to the point of junction between the resistors 66 and 67.While the voltage of the battery 58 is high enough to operate themeasuring circuits reliably, the Zener diode 65 is conductive andsufficient voltage is developed across the resistor 67 to provide therequired bias to the base of the transistor 61 to make it conductive inresponse to operation of the Schmitt trigger circuit. As the voltage ofthe battery drops, the Zener diode 65 quits conducting before the Zenerdiode 63 becomes nonconductive and removes the operating bias from thetransistor 61. Since a reading cannot be obtained on the moisturetester, the operator realizes that a new battery ought to be installed.

The grain moisture of this invention is reliable and is easily portablefor carrying to various locations where grain needs to be tested. Thetemperature compensation aids in providing accurate readings at varioustemperatures encountered where material is to be tested. The integrationof the scale for measuring the samples aids in quick, accuratemeasurements of moisture content. The table showing moisture content forthe readings obtained on the dial 39 is readily applied to the outersurface of the tester for easy quick reference.

What is claimed is:

1. A grain moisture tester comprising a test cell having a cylindricalcontainer constituting an outer electrode and a cylindrical conductorconstituting an inner electrode mounted coaxially within said containerand insulated therefrom, an insulator closely surrounding thecylindrical wall of said inner electrode to simulate an air gap, thedielectric constant of said insulator being substantially one, the ratio.of thickness of said insulator and the outside radius of said innerelectrode being approximately 1:1 1 and means connected electrically tosaid electrodes for measuring permittivity of a sample placed betweensaid electrodes.

2. A grain moisture tester as claimed in claim 1 in which said insulatoris made of closed-cell polystyrene foam.

3. A grain moisture tester comprising a test cell having a firstcylindrical container constituting an outer electrode and a cylindricalconductor constituting an inner electrode mounted within said firstcontainer and insulated therefrom, a spring scale having a mountingmember, an elongated scale member and a spring, said scale member havingan inner end slidably mounted within said mounting member, said springinterconnecting said mounting member and the inner end of said scalemember, means for securing said mounting member coaxially within saidcylindrical conductor to extend the outer end of said scale membercoaxially upwardly from said first container, and electrical circuitmeans connected to said electrodes for measuring permittivity of asample placed between said electrodes, said grain moisture tester havinga second cylindrical container, said electrical circuit means formeasuring permittivity being mounted within said second container, thebottom portion of said first container being mounted within the topportion of said second container, said first container having spacedabove its bottom a disk of insulating material as a bottom of thatportion of the test cell to hold a sample to be tested, the bottom ofsaid first container having a concentric opening, plug-in connectingmeans having a portion secured to said disk and connected to said innerelectrode and a mating portion secured to said circuit means within saidsecond container, said connecting means extending through the center ofsaid concentric opening to provide conduction from said inner electrodeto said circuit means, the spacing between said bottom of said secondcontainer and said connecting means being sufficient to preventsignificant stray capacitance therebetween. 1

4. A grain moisture tester as claimed in claim 3 wherein said electricalcircuit means includes signal generating means and a resistor, saidresistor and said test cell being serially connected in the output ofsaid signal generating means, and voltage measuring means connected tosaid test cell for measuring the voltage developed thereacross.

5. A grain moisture tester as claimed in claim 4 wherein atemperature-compensating capacitor is connected in parallel with theelectrodes of said test cell and mounted within said portion of saidtest cell to receive a sample.

6. A grain moisture tester as claimed in claim 4, wherein said voltagemeasuring means includes a Schmitt trigger circuit having an inputresponsive to application of alternating-current voltage to cause it tochange state for each peak of said applied voltage above a thresholdvalue, alternating-current amplifier means connecting said test cell andthe input triggering circuit of said Schmitt trigger, and indicatingmeans connected to the output of said trigger circuit to show theoperation thereof.

7. A grain moisture tester as claimed in claim 4 wherein said electricalmeasuring means includes a low-voltage disabling circuit, a source ofvoltage connected to supply power to said electrical measuring means,said voltage measuring means including an indicator circuit, atransistor having an input control circuit and an output circuit, saidoutput circuit being connected through said indicator circuit to saidsource of voltage, means connected between said test cell and said inputcontrol circuit to apply control signal to said input control circuit inresponse to the voltage developed across said test cell exceeding apredetermined amount, biasing means including a serially connectedbreak-down diode and a resistor connected across said source of voltage,said biasing means also being connected to said input control circuit,said break-down diode normally being conductive to provide the properbias to said transistor to make it conductive in response to saidvoltage across said test cell exceeding said predetermined amount, saidindicator operating in response toconduction through said transistor,and said break-down diode becoming nonconductive in response to thevoltage supplied by said source of voltage dropping below apredetermined desirable amount for operating said electrical measuringmeans, thereby preventing conduction through said transistor andpreventing operation of said indicator.

8. A grain moisture tester as claimed in claim 7 having an insulatorclosely surrounding the cylindrical wall of said inner electrode thedielectric constant of said insulator being substantially one and itsthickness being sufficient to prevent substantial concentration ofelectric field near said inner electrode as a result of unavoidableunevenness in the packing of a sample placed between said electrodes,said means connected between said test cell and said input controlcircuit including a Schmitt trigger circuit having an input responsiveto application of alternating-current voltage to cause it to changestate for each peak of voltage above a threshold amount.

9. A grain moisture tester comprising a test cell having a cylindricalcontainer constituting an outer electrode and a cylindrical conductorconstituting an inner electrode mounted coaxially within said containerand electrically insulated therefrom, circuit means connected to saidelectrodes for measuring the permittivity of a sample placed betweensaid electrodes, a chassis attached to the bottom of said test cell as abase therefor, said circuit means being mounted within said chassis, anda spring scale permanently fastened to said test cell and calibrated todetermine the weight of a sample contained within the cell by weighingsaid grain moisture tester as a unit, said spring scale comprising acoil spring, an elongated scale member, and a handle, said coil springand the lower end of said elongated scale member being disposed in saidcylindrical conductor, the lower end of said coil spring being fastenedto the lower end of said cylindrical conductor, the upper end of saidcoil spring being connected to the lower end of said elongated scalemember, the upper end of said elongated scale member protruding upwardlyfrom the upper end of said cylindrical conductor, and said handlefastened to the upper end of said elongated scale member.

10. A grain moisture tester as claimed in claim 9 in which a swivel isconnected in a series with said coil spring between the lower end ofsaid elongated scale member and the upper end of said coil spring.

11. A grain moisture tester comprising first and second spacedelectrodesbetween which grain is placed to determine its moisturecontent, a signal generator having its output connected to saidelectrodes for applying alternating current through the capacitor formedby said electrodes, a transistor having an input control circuit and anoutput circuit, voltage threshold sensing means having an inputconnected to said electrodes and an output connected to said inputcontrol circuit of said transistor, a source of voltage connected tosupply power to said signal generator and to said threshold sensingmeans, an indicator connected to the output of said transistor, saidtransistor normally operating between a nonconductive condition and aconductive condition in response to the voltage level across said cellpassing through a predetermined level sensed by said voltage thresholdsensing means and thereby operating said indicator to show saidthreshold level, biasing means including a serially connected break-downdiode and a resistor connected across said source of voltage, saidbiasing means also being connected to said input control circuit of saidtransistor, said break-down diode normally being conductive to applyrequired bias to said transistor to make it operative in response to thevoltage across said cell passing through said predetermined level, andsaid break-down diode becoming nonconductive in response to the voltagesupplied by said source of voltage dropping below a predetermineddesirable amount for operating said signal generator and said thresholdsensing means, thereby preventing conduction through said transistor andoperation of said indicator.

12. A grain moisture tester as claimed in claim 11 wherein saidthreshold sensing means includes an alternating-current amplifier and aSchmitt trigger circuit, said alternating-current amplifier means havingan input connected to said electrodes and an output connected to theinput control circuit of said Schmitt trigger circuit, the output ofsaid Schmitt trigger circuit being connected to said input control ofsaid transistor, and said trigger circuit being responsive toapplication of alternating-current voltage from said amplifier means tocause it to change state for each peak of said applied voltage above athreshold amount.

13. A grain moisture tester as claimed in claim 12 having a resistor inseries with said electrodes, the output of said generator being appliedthrough said resistor to said electrodes.

UNITED STATES PATENT OFFICE CERTIFICATE CF CORRECTION Patent No. 3.72936Dated June 12, 1973 Inventor(s) y 11 It is certified that error appearsin the above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 3, line 30, after "insulator" insert 0 variations line LLO,change "variation" to Column 5, line L l, after "a'r'rri" insert of 7Column 10, claim 12, line 26, after "control" insert circuit Signed andsealed this 26th day of March 197A.

(SEAL) Attest:

EDWARD I LFLETCHERJR. C. MARSHALL DANN Commissioner of Patents AttestingOfficer FORM PC4050 USCOMM-DC some-P69 UTS. GOVERNMENT PRINTING OFFICEI969 0-366-334,

1. A grain moisture tester comprising a test cell having a cylindricalcontainer constituting an outer electrode and a cylindrical conductorconstituting an inner electrode mounted coaxially within said containerand insulated therefrom, an insulator closely surrounding thecylindrical wall of said inner electrode to simulate an air gap, thedielectric constant of said insulator being substantially one, the ratioof thickness of said insulator and the outside radius of said innerelectrode being approximately 1:11 and means connected electrically tosaid electrodes foR measuring permittivity of a sample placed betweensaid electrodes.
 2. A grain moisture tester as claimed in claim 1 inwhich said insulator is made of closed-cell polystyrene foam.
 3. A grainmoisture tester comprising a test cell having a first cylindricalcontainer constituting an outer electrode and a cylindrical conductorconstituting an inner electrode mounted within said first container andinsulated therefrom, a spring scale having a mounting member, anelongated scale member and a spring, said scale member having an innerend slidably mounted within said mounting member, said springinterconnecting said mounting member and the inner end of said scalemember, means for securing said mounting member coaxially within saidcylindrical conductor to extend the outer end of said scale membercoaxially upwardly from said first container, and electrical circuitmeans connected to said electrodes for measuring permittivity of asample placed between said electrodes, said grain moisture tester havinga second cylindrical container, said electrical circuit means formeasuring permittivity being mounted within said second container, thebottom portion of said first container being mounted within the topportion of said second container, said first container having spacedabove its bottom a disk of insulating material as a bottom of thatportion of the test cell to hold a sample to be tested, the bottom ofsaid first container having a concentric opening, plug-in connectingmeans having a portion secured to said disk and connected to said innerelectrode and a mating portion secured to said circuit means within saidsecond container, said connecting means extending through the center ofsaid concentric opening to provide conduction from said inner electrodeto said circuit means, the spacing between said bottom of said secondcontainer and said connecting means being sufficient to preventsignificant stray capacitance there-between.
 4. A grain moisture testeras claimed in claim 3 wherein said electrical circuit means includessignal generating means and a resistor, said resistor and said test cellbeing serially connected in the output of said signal generating means,and voltage measuring means connected to said test cell for measuringthe voltage developed thereacross.
 5. A grain moisture tester as claimedin claim 4 wherein a temperature-compensating capacitor is connected inparallel with the electrodes of said test cell and mounted within saidportion of said test cell to receive a sample.
 6. A grain moisturetester as claimed in claim 4, wherein said voltage measuring meansincludes a Schmitt trigger circuit having an input responsive toapplication of alternating-current voltage to cause it to change statefor each peak of said applied voltage above a threshold value,alternating-current amplifier means connecting said test cell and theinput triggering circuit of said Schmitt trigger, and indicating meansconnected to the output of said trigger circuit to show the operationthereof.
 7. A grain moisture tester as claimed in claim 4 wherein saidelectrical measuring means includes a low-voltage disabling circuit, asource of voltage connected to supply power to said electrical measuringmeans, said voltage measuring means including an indicator circuit, atransistor having an input control circuit and an output circuit, saidoutput circuit being connected through said indicator circuit to saidsource of voltage, means connected between said test cell and said inputcontrol circuit to apply control signal to said input control circuit inresponse to the voltage developed across said test cell exceeding apredetermined amount, biasing means including a serially connectedbreak-down diode and a resistor connected across said source of voltage,said biasing means also being connected to said input control circuit,said break-down diode normally being conductive to provide the properbias to said transistor to make it conductive in response to saidvoltage acrosS said test cell exceeding said predetermined amount, saidindicator operating in response to conduction through said transistor,and said break-down diode becoming nonconductive in response to thevoltage supplied by said source of voltage dropping below apredetermined desirable amount for operating said electrical measuringmeans, thereby preventing conduction through said transistor andpreventing operation of said indicator.
 8. A grain moisture tester asclaimed in claim 7 having an insulator closely surrounding thecylindrical wall of said inner electrode the dielectric constant of saidinsulator being substantially one and its thickness being sufficient toprevent substantial concentration of electric field near said innerelectrode as a result of unavoidable unevenness in the packing of asample placed between said electrodes, said means connected between saidtest cell and said input control circuit including a Schmitt triggercircuit having an input responsive to application of alternating-currentvoltage to cause it to change state for each peak of voltage above athreshold amount.
 9. A grain moisture tester comprising a test cellhaving a cylindrical container constituting an outer electrode and acylindrical conductor constituting an inner electrode mounted coaxiallywithin said container and electrically insulated therefrom, circuitmeans connected to said electrodes for measuring the permittivity of asample placed between said electrodes, a chassis attached to the bottomof said test cell as a base therefor, said circuit means being mountedwithin said chassis, and a spring scale permanently fastened to saidtest cell and calibrated to determine the weight of a sample containedwithin the cell by weighing said grain moisture tester as a unit, saidspring scale comprising a coil spring, an elongated scale member, and ahandle, said coil spring and the lower end of said elongated scalemember being disposed in said cylindrical conductor, the lower end ofsaid coil spring being fastened to the lower end of said cylindricalconductor, the upper end of said coil spring being connected to thelower end of said elongated scale member, the upper end of saidelongated scale member protruding upwardly from the upper end of saidcylindrical conductor, and said handle fastened to the upper end of saidelongated scale member.
 10. A grain moisture tester as claimed in claim9 in which a swivel is connected in a series with said coil springbetween the lower end of said elongated scale member and the upper endof said coil spring.
 11. A grain moisture tester comprising first andsecond spaced electrodes between which grain is placed to determine itsmoisture content, a signal generator having its output connected to saidelectrodes for applying alternating current through the capacitor formedby said electrodes, a transistor having an input control circuit and anoutput circuit, voltage threshold sensing means having an inputconnected to said electrodes and an output connected to said inputcontrol circuit of said transistor, a source of voltage connected tosupply power to said signal generator and to said threshold sensingmeans, an indicator connected to the output of said transistor, saidtransistor normally operating between a nonconductive condition and aconductive condition in response to the voltage level across said cellpassing through a predetermined level sensed by said voltage thresholdsensing means and thereby operating said indicator to show saidthreshold level, biasing means including a serially connected break-downdiode and a resistor connected across said source of voltage, saidbiasing means also being connected to said input control circuit of saidtransistor, said break-down diode normally being conductive to applyrequired bias to said transistor to make it operative in response to thevoltage across said cell passing through said predetermined level, andsaid break-down diode becoming nonconductive in response to the voltagesupplied by saId source of voltage dropping below a predetermineddesirable amount for operating said signal generator and said thresholdsensing means, thereby preventing conduction through said transistor andoperation of said indicator.
 12. A grain moisture tester as claimed inclaim 11 wherein said threshold sensing means includes analternating-current amplifier and a Schmitt trigger circuit, saidalternating-current amplifier means having an input connected to saidelectrodes and an output connected to the input control circuit of saidSchmitt trigger circuit, the output of said Schmitt trigger circuitbeing connected to said input control of said transistor, and saidtrigger circuit being responsive to application of alternating-currentvoltage from said amplifier means to cause it to change state for eachpeak of said applied voltage above a threshold amount.
 13. A grainmoisture tester as claimed in claim 12 having a resistor in series withsaid electrodes, the output of said generator being applied through saidresistor to said electrodes.